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anybody care to crunch the numbers? is it even possible to figure this out mathematically?

If you know the BTU loss/hour of the igloo walls, the heat output of the candle BTU/hour, you'll know whether the candle will gain on the igloo. Once you figure out if the candle gains, you can then divide the gain by how many BTUs it will take to heat the air from -40 to 0. Then you know how many hours it will take for the igloo to get warm. And finally, the question is will the candle last long enough to get there.

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assuming that an igloo is 1/2 a sphere, the volume of a sphere is 4/3 pi x radius cubed, with a 5' radius, that works out to 524 cu ft, half it and we get 262 cubic feet. The r-value for snow is approximately r=1 for each inch, say twelve inch thick walls the iglue would have an r-value of 12. a 1 pound candle is equivalent to 361 BTUs

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2 full grown men at rest give off about 230 BTU's per hour, with a candle giving off 361 BTU's per hour we have a delta T of 72 degrees.... alot but our room is only 262 cubic feet a few more minutes....

to raise 1 lb of air 1 degree you need .24 BTU's, 1 pound of air is approximately 13.3 cubic feet. Given our igloo is about 262 cubic feet, inside there is about 19.69 pounds of air, 4.73 BTU's are required to raise the temperature 1 degree per hour. Our heating output is about 821 BTU's per hour, so our temperature will go up at about 37 degrees per hour, so in about 2 hours the room will be up to 34 degrees. assuming loss I would say yes it is possible for 2 hunters and a candle to heat an iglu to above freezing in about 2 and a half hours, with a temperature rise of about 30 degrees per hour... I know I made thes MUCH more complicated than I had too!!

2 full grown men at rest give off about 230 BTU's per hour, with a candle giving off 361 BTU's per hour we have a delta T of 72 degrees.... alot but our room is only 262 cubic feet a few more minutes....

to raise 1 lb of air 1 degree you need .24 BTU's, 1 pound of air is approximately 13.3 cubic feet. Given our igloo is about 262 cubic feet, inside there is about 19.69 pounds of air, 4.73 BTU's are required to raise the temperature 1 degree per hour. Our heating output is about 821 BTU's per hour, so our temperature will go up at about 37 degrees per hour, so in about 2 hours the room will be up to 34 degrees. assuming loss I would say yes it is possible for 2 hunters and a candle to heat an iglu to above freezing in about 2 and a half hours, with a temperature rise of about 30 degrees per hour... I know I made thes MUCH more complicated than I had too!!

do you want the inside temp of the igloo to go above 32/0 degrees f/c?

You probably don't want your igloo to melt on you, because being wet would be no fun.

On the other hand, I wonder if this would cause a negative feedback loop. If the igloo starts to melt, you would presumably reduce the R-value of the igloo. This would increase your heat loss, and probably start to re-freeze some of the slushy snow into ice. I'm not sure this would work out, but it doesn't seem entirely implausible either.

Do you know of people who have melted their igloos?

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I have killed enough time this morning with this, I dont think that we would want the temp to raise above 32 degrees just as was pointed out. But then again I dont know, there is just too many variables goo one for a thermo dynamics class!